The dynamic testing of bodies intended for use in a non-gravitational environment is greatly complicated by the fact that the testing must be accomplished on earth where there is a gravitational field. Unfortunate experiences have shown that dynamic responses in space can differ greatly from those which are encountered on earth. Still, space is not the place to conduct interim dynamic testing of basic structures. It is far too expensive and is likely to provide only a single test which might not provide the necessary information. Instead what is required is a support structure which within sensible limitations of dynamic and dimensional ranges, and cost, can provide support for a body under test which will be the equivalent of the body's response to forces exerted outside of a gravitational field.
Evidently the body under test must be physically supported, and it will be, by means of a spring suspension. However, this suspension is so constructed and arranged that, while still supporting the body, it exhibits a zero spring rate response to limited movements of the body. This characteristic provides behavior of the total system such that an absence of gravitational forces is simulated.
The zero rate response is well-known in the fields in which it is of interest, and there are at least several basic schemes for attaining this result. The inventor herein does not claim to be the inventor of any zero rate system, including the one described herein.
The problem with all of these systems is that the range of movement within which the zero rate effect exists is quite short. The inventor herein has been able to extend this range to a total movement of about 2.0 inches. Accordingly, to take advantage of this property of the system, it is important that, under the intended test load, the suspension be adjusted so the system is in a central datum position, preferably within a few thousandths of an inch of its very center.
These systems are expected to carry substantial loads. An installation with perhaps 30 of these suspensions, each supporting 100 to 750 pounds of weight, is well within the expected parameters of such installations.
Because there is zero spring rate at the datum position, the support condition can gently and very slowly drift. For this reason, adjustment is a slow and painstaking process which requires hours, and sometimes even days. At least to applicant's knowledge there does not exist any automatic and reliable means to accomplish this painstaking process.
It is an object of this invention to provide adjustment means for a zero spring rate system which is automatic in the sense of providing means to hunt for a center adjustment. Clearly the adjustment system itself cannot involve a springing response, or the system would have no tendency to stop. This invention intends to provide an adjustment means devoid of springing response.